This invention relates to an apparatus and method for controlling a land vehicle. In particular, but not exclusively, the invention relates to such an apparatus and method for automatically controlling a vehicle. The invention relates to the controlling of on- and off-highway vehicles, especially excavators or agricultural tractors. Mechanized tractors have been widely used in agriculture, approximately since the commercialization of internal combustion engines. The introduction of mechanized tractors revolutionized farming in the sense that a tractor permits a small number of workers to carry out what would otherwise be labor-intensive operations, at comparatively high speeds.
For many years, tractor designers have concentrated their efforts on improving the efficiency of parts of tractors over which tractor operators have no influence during use of the machines.
Thus, for example, there have been numerous efforts directed towards improving the combustion efficiency of tractor engines; to providing a choice of gear ratios suitable for particular agricultural tasks; and to improving the performance of tractor wheel/tire combinations for particular types of farming. Such efforts have resulted in improvements in tractor performance throughout the Twentieth Century. However, it is now suspected that the scope for obtaining further improvements in farming efficiency by concentrating on individual sub-systems of tractors may be limited.
Patent no. GB 253566 discloses a closed loop control system for adjusting the position of a tillage implement such as a plough by altering the height of the implement on a four bar linkage. The control strategy involved constantly adjusting the implement depth in order to maintain a constant draught (i.e. the force needed to pull the implement through the soil). The basic principles of GB 253566 are found in virtually all modern tractor mounted implement combinations, albeit with the mechanical components originally proposed replaced by electro-hydraulics or, increasingly commonly, microprocessor based control hardware.
In recent years, there have been moves to devise tractor control systems that attempt further to minimize the effects of the tractor operator's performance on the tractor's performance. The primary need for such systems arises when tractors are required to carry out operations, such as tilling of soil, with high accuracy and as rapidly as possible.
However, the majority of previous investigations attempt to automate only part of the operation of a tractor. The few previous attempts at automating virtually the entire operation of a tractor have hitherto failed. Thus there remains a need for an automated control system that removes from the working operations of the tractor as much as possible of the performance variability that can arise from actions of the tractor driver.
A tractor is a complex machine that is required to carry out a variety of tasks in widely differing physical conditions. Thus it would be desirable for any tractor control system to take account of variations in the sub-systems of the tractor/implement combination itself; variations in prevailing conditions; and the task required of the tractor/implement combination at any given time.
The variable sub-systems of the tractor include the following:
1. depending on the engine type, engine throttle setting or engine speed governor setting; PA1 2. transmission ratio selected; PA1 3. the setting of an adjustable implement hitch and/or the settings of the variable elements of an attached implement or accessory. PA1 1. implement working depth; and PA1 2. implement working width (when this is adjustable). PA1 1. the soil specific resistance (ie. the resistance per unit area of the soil to cultivation or fracture). This determines, in conjunction with the other variable factors, the so-called "draught" of the implement; PA1 2. the percentage slip at the vehicle driven wheels (i.e. the efficiency of the tractive effort at the wheel/soil interface); PA1 3. the pull (i.e. force) measurable at the implement hitch; and PA1 4. the forward speed of the vehicle. PA1 a programmable controller including stored therein data representative of a reference model of the vehicle's performance; PA1 one or more slave controllers respectively operatively connectable to a plurality of controllable sub-systems of a said vehicle, and operatively connected to the programmable controller; PA1 one or more sensors, operatively connected to the programmable controller, for detecting the performance of said controllable sub-systems; and PA1 a comparator for comparing the detected performance of the said controllable sub-systems and the reference model, the controller being operable to control the said sub-systems in dependence on an output of the comparator, characterized in that the reference model is a steady-state model, whereby to permit coordinated, automated control of all the said sub-systems. PA1 engine performance data; PA1 selected vehicle transmission ratio data; PA1 vehicle tractive efficiency data; and PA1 data on the setting of a vehicle-powered implement. PA1 soil type; PA1 initial vehicle axle loads; PA1 vehicle tire dimensions; and PA1 vehicle tire coefficients of rolling resistance (eg. front and rear coefficients). PA1 an engine output controller; PA1 a transmission ratio selector; PA1 an adjustable implement controller; and PA1 a tractor implement hitch controller. PA1 an engine output controller; PA1 a transmission ratio selector; PA1 an adjustable implement controller; and PA1 a vehicle implement hitch controller. PA1 a cultivation implement; PA1 a crop establishment implement; PA1 a material application implement; PA1 a crop harvesting implement; and PA1 a materials handling implement. PA1 initiating a control apparatus in particular as defined hereinabove; PA1 inputting into the control apparatus a set value of an adjustable characteristic of the implement; and PA1 subsequently operating the vehicle under the control of the control apparatus, the control apparatus maintaining the adjustable characteristic of the implement at said set value while simultaneously automatically adjusting one or more sub-systems of the vehicle in order to optimize a performance parameter of said vehicle. PA1 operating the vehicle whereby to record in the control apparatus one or more characteristics of operation of the vehicle under contemporaneously prevailing conditions.
The variable elements of the implement will depend on the type of implement and the use to which it is put. For a tillage implement such as a plough, some relevant variables may include:
Further variables that are of particular significance in tillage operations include:
Thus it will be seen that any control apparatus for automating all the controllable variables of a tractor/implement combination other than the steering (which in field conditions may ultimately prove impossible to automate) will necessarily be complicated.
EP-A-0070833 (Massey Ferguson Services NV) discloses optimization of the sub-systems of a tractor, using a central processor and a feedback loop. However, there is in the arrangement of EP-A-0070833 a necessary passivity in the system in the sense that an operator must specify various parameters such as the implement position (depth); the throttle setting; and the mode of optimization. (This can be selected eg. from a list including maximization of work rate and minimization of fuel consumption.)
Thus the arrangement of EP-A-0070833 is not a fully automatic control scheme since the controller does not seek to maximize the tractor performance in dependence on measured values eg. of soil strength, etc; but instead seeks to maximize the performance criteria against set values input by the driver. Such set values may or may not represent optima under the conditions prevailing at the time of use of the tractor.
In any event, the control scheme of EP-A-0070833 is not adaptive, since the apparatus cannot take account of changes in the field conditions over time.
The paper "Control Concept for a Tractor Management System" (LandTechnik, 50(2) 1995 pages 76 to 77) concerns a tractor optimization system that is integrated in the sense of controlling the transmission, engine output and implement. The arrangement disclosed employs a dynamic reference model of the optimization criteria stored in eg. the non-volatile memory (NVM) of a CPU. In other words, the reference model in the LandTechnik paper includes higher order physical variables. Thus the model includes data on accelerations, inertias and how they change with e.g. changing vehicle speed; and so on.
As in the arrangement of EP-A-0070833, in the arrangement disclosed in the LandTechnik paper the implement position, throttle setting, transmission ratio and type of work have to be input by the tractor operator before the system will attempt to optimize the tractor performance.
It may theoretically be possible to modify the arrangement disclosed in the LandTechnik paper to provide a fully automatic system in which e.g. the soil strength, and hence the variables dependent therefrom, are determined by the CPU. However, the authors of the paper suggest that in practice it will prove impossible to attain complete automation of tractor control systems using mathematical-physical reference models.
This view is believed to derive from the use in the LandTechnik paper of a dynamic reference model. Such a model is likely to be highly complex, and hence to require significant computing power to implement. Also, of course, dynamic models require data on e.g. accelerations, inertias, spring constants and other physical aspects of the tractor system that influence the tractor performance during use. Very often such measurements are in practice completely impossible to make, partly because of the inherently closed nature of some sub-systems of a tractor. This in turn would lead to the use of estimated values for such measurable variables. Unless such estimations could be made with complete confidence as to their accuracy, there is a risk of introducing errors into the dynamic model. The effects of such errors tend to multiply in use of dynamic models and could lead the performance of the control system to be worse than that of an operator driving a tractor/implement combination having no control systems.
Thus there are significant disadvantages associated with the use of a dynamic reference model in integrated, automatic control of tractor sub-systems.
U.S. Pat. No. 4,208,929 discloses an electronically controlled transmission system suitable for use in a tractor. Although this control system takes account of some measurable aspects of tractor performance, the control scheme disclosed does not operate on all the sub-systems of the tractor/implement combination in an integrated way, to provide automatic operation of tractor control.
FR-A-2723792 discloses a control system for a tractor/implement combination that seeks to optimize the vehicle performance during, e.g ploughing operations. The control program includes so-called "static" data, i.e. pre-recorded cartographical data on the field conditions likely to be encountered by the tractor/implement combination. However, the static data in FR-A-2723792 does not function as a reference model of the tractor/implement combination. In other words, the control program in FR-A-2723792 is not capable of modifying the settable parameters of the tractor/implement combination in real time, in dependence on instantaneously prevailing field conditions.
Also, there remains a need in FR-A-2723792 for the operator to input various data, such as the soil type, the characteristics of the implement, and a work criterion such as maximizing of fuel economy, maximizing work rate, and so on.
U.S. Pat. No. 4,267,569 discloses control of a motor vehicle diagnostic system. U.S. Pat. No. 4,747,301 discloses an automated performance monitor; U.S. Pat. No. 4,594,666 discloses a transmission control apparatus; U.S. Pat. No. 5,260,875 discloses an automated crop spraying system; and U.S. Pat. No. 5,305,215 discloses an expandable microprocessor system for an off-highway vehicle. However, none of the foregoing publications discloses what may truly be said to be an integrated control system for a vehicle such as a tractor/implement combination or an excavator.
Similarly, U.S. Pat. No. 4,098,346 discloses control of part of a tractor/implement combination sub-system (ie. the plough width); and U.S. Pat. No. 4,141,419 discloses a control system for controlling the approach angle of a plough unit in response to speed variations.
DE-A-4113191 and DE-A-3720334 disclose methods of adjusting the widths of plough bodies to take account of localized conditions, and U.S. Pat. No. 4,062,410 discloses an adjuster for the plough bottom.
U.S. Pat. No. 4,646,849 discloses an automatic controller for a reversible plough body, whereby the plough width is adjusted at the same time as the plough is reversed.
Finally, U.S. Pat. No. 4,778,013 discloses an apparatus for adjusting the angle of the mould boards of a series of plough bodies in response to the tractive force required to drive the plough through soil.
None of the foregoing disclosures discloses anything other than the control of an isolated sub-system of a tractor/implement combination.